DoubleClick caught supplying malware-tainted ads

'Your PC is hosed. Click here to fix'

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Updated DoubleClick, the massive internet advertising platform that recently agreed to be bought by Google, has been caught serving rogue ads designed to trick users into buying unneeded software, according to an article on eWeek.

The maliciously crafted ads originated with an outfit known as AdTraff.com. After holding itself out as a legitimate online advertiser, AdTraff tricked name-brand websites including CNN, The Economist, The Huffington Post and the official site of the Philadelphia Phillies baseball team to sign contracts to run ads, according to a DoubleClick manager. The publishers at these sites then uploaded the ad files to DoubleClick servers, which distributed the banners to end users.

The ads contain encrypted links to malicious code that causes authentic-looking security warnings to be displayed on an end user's computer in an attempt to dupe the person into buying software that will fix the problem.

Sean Harvey, a senior product manager for DoubleClick, said the company is working hard to prevent its servers from serving such ads in the future. In the past three months, engineers have deployed a monitor that inspects every ad in DoubleClick's database in real time.

"We are running a constant scanning process on our system and we regularly find stuff that doesn't get turned on because we find problems," he told The Register. "Because you're putting it into the DoubleClick system, we feel it's our responsibility to run 24-hour scans for malware or malicious links."

eWeek's report comes less than a week after a researcher for SecureWorks warned that thousands of PC users had been duped by anti-spyware ads that had appeared on hundreds of websites in recent weeks.

Malicious code hardwired into the ads prompted a pop-up that warned of a bogus security threat on the visitor's machine. It offered to fix the problem in exchange for as much as $80. The ad then attempted to install software on the victim's machine that is difficult to remove.

Jackson said Monday that malicious ads are continuing to be served on high-trafficked websites, which he declined to identify by name.

The rogue ads were served by DoubleClick as recently as Sunday, according to eWeek, which cited researchers from Sunbelt Software. The publication said the malware being pushed is a variant of WinFixer, a piece of malware that poses as a diagnostic tool. It provides a fake alert that tricks people into spending money on software to fix the problems.

In addition to stepping up monitoring of the ads it serves, DoubleClick is also calling on publishers to take steps to prevent malicious ads from being served to end users. Web sites need to carry out more due diligence when approached by unfamiliar advertisers, and they also need to vet ads for suspicious code and links before uploading them to DoubleClick servers, Harvey said. He called rogue ads "an industry-wide challenge."

Indeed, the scams described by eWeek and SecureWorks are the latest to piggyback on banner ads that are fed to popular destinations. Other networks that have distributed toxic banners include Real Media and the Yahoo!-owned Right Media. Ad networks are ideal carriers for malicious payloads because of their massive reach and because they catch people as they surf to sites they know and trust.

On Monday, website marketing pros flooded industry email lists with reports of reader complaints who said they have been receiving inappropriate ads. The pros said ad servers for sites including The Wall Street Journal, Discovery and BizJournals had been hijacked, according to eWeek.

In addition to AdTraff.com, Jackson named at least three other outfits he believes have also fed malicious ads to large sites in recent weeks. They include ForceUp, BlessedAds and Traveltray.

Many of the groups have overlapping executives and pose as legitimate ad networks that are interested in buying ad space from large websites, said Jackson, who added that their combined reach has been substantial.